The invention relates generally to a system for storing slack cable and, more particularly, to a slack storage system that stores slack cable underneath a fiber optic cable access terminal or pedestal and also provides support for the terminal or pedestal.
Demand for increased communications bandwidth has encouraged construction of telecommunications networks in which fiber optic cable is used for transmission directly to a telecommunications subscriber's premises, rather than running copper wire to the premises, as has been used in the past. In a community with a fiber optic network, multi-fiber underground distribution cable is commonly installed by plowing it through the area to be served, and splicing the distribution cable into individual fiber cables that continue to each subscriber.
In a typical situation, the distribution cable that runs through a residential neighborhood might have one or two splice points on each block. Each of the subscriber residences on that block would be connected to the fiber optic system by a single fiber cable running from the home or business to the splice point.
Fiber optic cable splicing is most often done in an enclosed trailer that houses the specialized equipment in a controlled environment. Splicing requires there to be adequate slack cable available at each splicing location to reach the trailer. On early fiber to the home projects, slack cable has been stored by installing a relatively expensive and heavy precast vault that also housed the splice itself. These vaults had earlier been used to house the splices in fiber optic trunk transmission lines connecting cities. This approach, however, requires that the splice be protected from ground water in an expensive housing, and does not lend itself to adding new subscriber lines.
More recently, the trend has been to house the splice in an above-ground fiber access terminal, an adaptation of the pedestals used for copper wire systems. These fiber access terminals offer the advantage of easy access to the distribution cable if additional subscribers are to be added, but do not offer enough storage space for slack cable to reach a splicing trailer. Designers have been forced to either use the expensive precast splicing vaults in connection with the fiber access terminals, or to forgo the slack storage, requiring that splicing be done at the terminal (instead of a splicing trailer) in less than ideal conditions. Additionally, when the slack cable is not available, it is more difficult, time consuming, and expensive to re-establish service in the event a distribution cable is cut.
When conventional precast splicing vaults are used for storage under the fiber access terminals, a rectangular opening is cut into the lid of the vault, and the pedestal is inserted into the opening. Because the vaults are traditionally open bottomed, it is a source of humidity, and is relatively warmer than the air in the pedestals during the fall and early winter. The warm, humid air rises into the pedestal and condenses, creating moisture, frost, and ice. This creates problems when the pedestal must be opened.
The previously used precast vaults were rectangular, and thus required that the material used in the vaults be sufficiently rigid to withstand the soil and vehicle approach loads.
Also, the previous storage vaults required that the pedestal be inserted into an opening cut into the lid of a precast vault, which was then installed with the lid at grade (ground) level. This meant that all drop cables installed had to be installed by running them under the edge of the vault, up through the vault with the distribution and branch cables. This method is less convenient than being able to bring a single drop cable into the pedestal by going through the sidewall or under the edge of the pedestal.
Because the lid of the vault used in previous methods had to be even with the ground, it was difficult to achieve a plumb installation of the pedestal if the ground surface at the pedestal location was steeply sloped.